In shearing-extruding trimming technology, the stress state of core deformation zone directly affects the surface quality of parts. The effects of punch-nose radii on stress state of core deformation zone have been studied through theoretical analysis, numerical simulation as well as physical experiments. The results indicate that the punch nose angle provides lateral and vertical extrusion to materials of core deformation zone and makes it in a state of compression. The compressive stress can inhibit the tear, so as to reduce the forming surface damage and improve the forming quality.